1. Field of the Invention
The present invention relates to a digital image signal recording/reproducing apparatus and a method thereof which, even in a long time mode such as a Long Play(LP) and Super Long Play(SLP), can maintain the same channel spacing of a tape as in a normal mode, so as to prevent crosstalk generated among the channels(tracks) when the channel spacing of the tape is narrowed in a long time mode.
2. Description of the Prior Art
Currently, a Video Cassette Recorder (VCR) is widely used as an image signal recording/reproducing apparatus.
Generally, the VCR records on a recording medium a signal inputted from a signal input source, such as a television or a video camera, and reproduce the signal recorded on the recording medium.
However, a broadcasting signal can also be directly received and recorded by equipping the VCR with a tuner.
Furthermore, because the length of the tape used as a recording medium in an image signal recording/reproducing apparatus such as the VCR is limited, a function for recording more information for a long period of time is necessary.
As a method to record the image signal on a limited recording medium for a long time in an analog method, the LP mode and SLP mode have been developed, which reduce a tape speed more than the standard play SP mode by 1/N, so that a recordable time can be increased by N times.
For example, the tape speed is reduced by 1/2 in the LP mode, doubling the recordable time compared to the SP mode.
The tape speed is reduced by 1/3 in the SLP mode, tripling the recordable time compared to the SP mode.
The standardized tape speed (SP) of the VHS VCR is 33.34 mm/s in the National Television System Committee NTSC color television system, and the speed is 23.39 mm/s in the Phase Alternation Line PAL system and the Sequential Couleur a Memoire SECAM system.
FIG. 1 is a constitutional diagram of a tape track in the SP mode of an image signal recording/reproducing apparatus.
In FIG. 1A, if the tape speed is assumed as V1, a track number per field as Tf, and a field number per second (generally 60 seconds) as Ts, a track interval A1 can be defined as in Formula (1). ##EQU1##
Therefore, a track width T1 can be obtained by the following formula (2). EQU T1=A1.multidot.Sin.theta.=V1.multidot.Sin.theta./(Ts .times.Tf)Formula (2)
In other words, it should be apparent that the track width T1 is in proportion to the speed V1 but is in an inverse proportion to the field number Ts.
Accordingly, in the conventional analog VCR, because the tape speed in the LP mode is reduced by 1/2(V2=V1/2) compared to tape speed of the SP mode as illustrated in FIG. 1B, the track width T2 of the LP mode is also reduced in width by 1/2(T2=T1/2) compared to the track width T1 of SP mode.
Therefore, long time recording is possible in the LP mode due to the narrowed track width of T2: however, due to increased crosstalks among the tracks, a problem arises in that the signal-to-noise S/N ratio deteriorates.
Furthermore, there is another problem in that separate heads for SP mode are required and for LP mode according to differences in the track widths.
FIG. 1C is an illustration showing a recording track pattern to be formed on a tape of a digital image signal recording/reproducing apparatus. In a conventional digital image signal recording/reproducing apparatus, an incoming image signal data of 1 field is divided into more than 2 tracks to thereafter be recorded. Accordingly, one frame of image signal data is divided into 4 tracks to be recorded. However, in some cases, the data is divided into 6 tracks to be recorded.
FIG. 2 is a constructional block diagram of a conventional digital image signal recording/reproducing apparatus. A data compressing unit 1 compresses an incoming image signal data.
In other words, a Discrete Cosine Transform (DCT) is performed on the image signal data, a DCT coefficient is quantized and then the data is again compressed utilizing a Huffman coding technique.
An error correction encoding unit 2 performs an error correction encoding on the image signal data compressed at the data compressing unit 1.
In the error correction encoding unit 2, the data compressed in the data compressing unit 1 is added with a vertical added value for every external code in row directions at the external error correction encoding unit(not shown). The image data added with the vertical added information to the external code is shuffled for every picture unit at a shuffling unit(not shown) and a horizontal added information is added for every internal code in column directions at an internal error correction coding unit (not shown).
A modulating unit 3 modulates an output of the error correction encoding unit 2. In the modulating unit 3, an image data encoded by the error correction and expressed in an 8-bit is modulated into an M bit in order to compensate for a high error rate against a low frequency signal of an encoded block.
A recording amplifier 4 amplifies an output of the demodulating unit 3 in order that the output can be recorded on the recording medium. A head drum 5 having a head records on the recording medium the signal amplified by the head at the recording amplifier 4. A reproducing amplifier 6 amplifies a signal reproduced from the head on the drum 5.
A demodulating unit 7 decodes an output of the reproducing amplifier 6. In other words, the data modulated to the M-bit is decoded into an original 8-bit data at the demodulating unit 7.
An error correction decoding unit 8 performs an error correction demodulating on the output of the decoding unit 7. In an internal error correction decoding unit(not shown), a correction is performed on a correctable error if an error occurs in the decoded data.
Uncorrectable errors are transmitted with an error flag, and a deshuffled data is arranged in an original order at a deshuffling unit(not shown).
A data transmitted along with the error flag is corrected at an external error correction decoding unit(not shown).
A data restoring unit 9 restores a data outputted and compressed from the error correction decoding unit 8 to an original data. Currently, there is no long time mode in the digital image signal recording/reproducing apparatus described above.
That is, if the tape speed is reduced by 1/N in the above digital image signal recording/reproducing apparatus in order to record for a long time, the track width becomes narrow to thereby increase the crosstalks among tracks, so that the S/N ratio deteriorates.